Generally, photosensitive printing plate is manufactured by coating the surface of the support such as aluminum plate, zinc plate, etc., with a photosensitive resin composition after roughening and making hydrophilic the support surface so as to intensify its adhesion to the photosensitive resin composition. The thus manufactured and commercially sold photosensitive printing plate is generally called PS plate.
Such photosensitive printing plate is smooth and flat on its surface, that is, the surface of the photosensitive layer formed from a photosensitive resin composition, so that when a flat original film is placed overlying said layer for effecting exposure and printing, it is found very difficult to purge air out of the space therebetween in a short period of time, and hence a long time would be required for bringing them into close contact with each other. Generally, the original film is placed on the photosensitive printing plate in a vacuum-type contact frame and the air trapped therebetween is sucked out by vacuum to bring them into close attachment. But since air usually stays in the form of independent cells in the non-peripheral areas of the two members, it would take long time to get rid of such air for ensuring close contact of said two members. If exposure is performed in an inperfect stage of contact, there can not be attained reproduction of a picture faithful to the original. For these reasons, reduction of the time required for attaining close contact has been a desideratum in the plate making industry.
As a solution to this problem, it was proposed to provide an uneven layer on the surface of the photosensitive printing plate. For instance, Japanese Patent Laid-Open Nos. 111102/76 and 29302/77 and U.S. Pat. No. 4,126,406 propose the methods for producing uneveness on the photosensitive layer surface by applying thereon a material which can be removed by a developing treatment. These methods, however, complicate the production process as one or more additional steps are involved, that is, the photosensitive composition is first applied on the support and, after drying thereof resin is printed thereon in an uneven pattern, followed by further drying.